556 dual timer problem

Ian Bell · 2009-12-04T16:43:05+00:00

I have used a 556 dual timer to build a motorbike indicator lights flasher for a friend. The first timer is arranged as a 30 second one shot which enables the second timer which is arranged as a 1 sec astable to flash the indicators. When the first timer is triggered, the second operates for about 30 secs - the circuit is straight out of the applications section of the data sheet. I have built two identical circuits, one for the left and one for the right indicators and operated by a SPDT momentary switch.There is one problem though. When it is first powered up, the one shot timers trigger and both the indicators flash for the 30 second interval. After that it functions as normal. When first starting up this is a minor inconvenience but if he stalls the bike and restarts then it happens again and as he says 'is a bloody pain in the ass'.So, is there a way to ensure the 30 second one shots do not trigger at power up?CheersIan

Dec 04, 2009 63 Replies

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Rich Grise 16 years ago

I'd use a transzorb instead of a zener - they're designed to absorb spikes; use one that's rated at about 7 or 8 V. I'd also use an inductor either instead of the R1 there, or in series with it.

I know about transzorbs - at one company where I worked, they had MOVs all over the place, and the service folks were continually going out to replace them, or they'd ship the box to us for warranty repair. Then one day, we discovered TransZorbs, and they worked so well that they issued an ECO (Engr. Change Order) _and_ an EMO (Engr. Mod. Order) to get rid of ALL the MOVs.

With just a zener, I'd see if there are any 5W zeners anywhere. Automotve (and bike) electrical systems are extremely harsh.

Cheers! Rich

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JosephKK 16 years ago

gold stuffed somewhere.

from?

Somebody enters it at a keyboard and poof all your money is devalued.

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ruffrecords 16 years ago

ain

I got the board back from my friend and I have applied the suggested reset mod. On the bench it works a treat. I'll get the board back to my motorcycling friend and hopefully that will be the cure.

Thanks for the many suggestions - I am now getting into PIC development - and a special thanks to Robert Baer who sent me a PICKit

2 from the US for no charge.

Cheers

Ian

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